Deshay Martin, brotherin-law of Mario Romero, who was slain outside his home by Vallejo police Sept. 2, attends a rally at a Solano County government building, where family members and the NAACP called on the U.S. Justice Department to investigate the killing and five officer involved shootings in Vallejo since May.

Photo: Carlos Avila Gonzalez, The Chronicle

Deshay Martin, brotherin-law of Mario Romero, who was slain outside...

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Family and friends of Mario Romero joined attorney John Burris, center, at a press conference where they called for an outside investigation into the fatal shooting of Romero in Vallejo, Calif., on Thursday, September 20, 2012.

The family of a man killed by Vallejo police officers while outside his home called on the U.S. Justice Department to investigate the shooting, one day after the city's mayor said he wants the state attorney general to open an inquiry.

Pressure has been mounting on Vallejo authorities over five officer-involved shootings since May. It intensified after the Sept. 2 killing of Mario Romero, 23, who police said reached for a weapon in his waistband as he got out of a car parked in front of his home.

Two officers fired 31 bullets at Romero and his passenger, who was wounded and later insisted Romero never stepped out of the car. Romero's weapon turned out to be a pellet gun, police said.

The incident sparked several public protests, including a Tuesday night ruckus that forced the Vallejo City Council to adjourn its meeting early.

"We have a department that is out of control," said George Holland, president of the NAACP's Oakland branch, who joined 30 protesters on the steps of a Solano County government building for Thursday's announcement. "If you can't be in a car in front of your home in this city without getting shot, what does that say about Vallejo?"

On Wednesday, Mayor Osby Davis took the unusual step of asking state Attorney General Kamala Harris to open an investigation. He cautioned that he had faith in investigations being conducted by police and the county district attorney, but said the public outcry suggested residents do not trust the system.

"Independent eyes will allow for complete transparency in order to rebuild the confidence of some citizens in the people who are sworn to protect and serve them," Davis said.

Despite the mayor's request, it could be months before state investigators scrutinize the shooting - if they do so at all. Officials said all local investigations need to be completed, followed by an official request from the Solano County district attorney's office for help.

Lynda Gledhill, a spokeswoman for the attorney general, said the office normally gets involved in cases only when there is a clear conflict of interest. "We have not been formally asked to do anything," she said.

Still, Davis' actions brought some relief to Romero's relatives, who said they still have not received his body from the coroner to conduct a funeral.

The family's attorney, John Burris, said he was delivering a letter to the U.S. Justice Department asking for a federal investigation of all of the recent officer-involved shootings in Vallejo to determine whether there was a "systemic pattern of use of deadly force" by police.

Burris, who represents the families of two of the five people killed by Vallejo officers this year, said Romero was hit by 13 bullets and disputed the officer's explanation of what led to the shooting.

"No African American in this country who is being pursued by police officers would reach into his waistband," Burris said. "When I heard that, I know it's a lie."